A driving status monitoring system for monitoring the driving status of a vehicle such as an automobile has been proposed. The driving status monitoring system includes: an image pickup device capable of taking an image of a driver's face and installed at a suitable place; and an image processing apparatus. The image pickup device takes an image of a driver's face, and the image processing apparatus detects, from image data obtained by taking the image, an eye position of the driver. Then, the image processing apparatus calculates the degree of opening of the eye (hereinafter, called an “opening”), and determines whether the opening is equal to or greater than a given threshold value, thereby recognizing an open/closed state of the eye. The threshold value is decided on the basis of a positional relationship between the installed site of the image pickup device and an object. With the use of the driving status monitoring system, the driver's drowsy driving may be detected, and a system for issuing an alarm to the driver conducting drowsy driving may be configured.
On the other hand, Patent Document 1 discusses that there has been proposed an image processing apparatus configured so that an opening when an upper eyelid is in an upwardly convex state is calculated, and a threshold value is set at a given percentage of the opening, e.g., at 70% of the opening, thus recognizing eye opening/closing.
Patent Document 1 discusses eye opening/closing detection adapting to differences among individuals.
However, the above-described conventional apparatus has a problem that eye recognition accuracy is degraded when an eye opening is changed due to a face orientation. For example, when a driver is facing downward, his or her eye is narrowed, resulting in false recognition of the closed state of the eye.
Further, since features such as shape and size of a facial part are generally changed due to a face orientation, the similar problem occurs even when a facial part other than an eye is recognized.    [Patent Document 1] Japanese Laid-Open Patent Publication No. 2006-251926